Ontogeny of osmoregulation and salinity tolerance in the gilthead sea bream Sparus aurata

An integrative perspective on fish health: Environmental and anthropogenic pathways affecting fish stress

Multifactorial studies assessing the cumulative effects of natural and anthropogenic stressors on individual stress response are crucial to understand how organisms and populations cope with environmental change. We tested direct and indirect causal pathways through which environmental stressors affect the stress response of wild gilthead seabream in Mediterranean costal lagoons using an integrative PLS-PM approach. We integrated information on 10 environmental variables and 36 physiological variables into seven latent variables reflecting lagoons features and fish health. These variables concerned fish lipid reserves, somatic structure, inorganic contaminant loads, and individual trophic and stress response levels. This modelling approach allowed explaining 30 % of the variance within these 46 variables considered. More importantly, 54 % of fish stress response was explained by the dependent lagoon features, fish age, fish diet, fish reserve, fish structure and fish contaminant load latent variables included in our model. This integrative study sheds light on how individuals deal with contrasting environments and multiple ecological pressures.

Stable isotope analyses of amino acids reveal the importance of aquatic resources to Mediterranean coastal hunter-gatherers

Determining the degree to which humans relied on coastal resources in the past is key for understanding long-term social and economic development, as well as for assessing human health and anthropogenic impacts on the environment. Prehistoric hunter-gatherers are often assumed to have heavily exploited aquatic resources, especially those living in regions of high marine productivity. For the Mediterranean, this view has been challenged, partly by the application of stable isotope analysis of skeletal remains which has shown more varied coastal hunter-gatherer diets than in other regions, perhaps due to its lower productivity. By undertaking a more specific analysis of amino acids from bone collagen of 11 individuals from one of the oldest and best-known Mesolithic cemeteries in the Mediterranean, at El Collado, Valencia, we show that high levels of aquatic protein consumption were achieved. By measuring both carbon and nitrogen in amino acids, we conclude that some of the El Collado humans relied heavily on local lagoonal fish and possibly shellfish, rather than open marine species. By contrast to previous suggestions, this study demonstrates that the north-western coast of the Mediterranean basin could support maritime-oriented economies during the Early Holocene.

Establishment and characterisation of single cell-derived embryonic stem cell lines from the gilthead seabream, Sparus aurata

An important bottleneck in fish aquaculture research is the supply and maintenance of embryos, larvae, juvenile and adult specimens. In this context, cell lines represent alternative experimental models for in vitro studies that complement in vivo assays. This allows us to perform easier experimental design and sampling and avoid the sacrifice of animals. Embryonic stem (ES) cell lines have attracted increasing attention because they have the capability to proliferate indefinitely and could be differentiated into any cell type of the organism. To minimise cell heterogeneity and increase uniformity of in vitro studies results, in this manuscript we report the development and characterisation of two single cell-derived ES cell lines (monoclonal) from the morula stage embryos of the gilthead seabream, Sparus aurata, named as SAEC-A3 and SAEC-H7. Both cell lines have been passaged for over 100 times, indicating the establishment of long-term, immortalised ES cell cultures. Sequence analyses confirmed the seabream origin of the cell lines, and growth analyses evidenced their high viability and proliferating activity, particularly in culture medium supplemented with 10-15% fetal bovine serum and 22 °C. Both cell lines showed the ability to generate embryoid bodies and show different sensitivity and response to all-trans retinoic acid. The analysis of epithelial (col1α1) and neuronal (sox3) markers in differentiated cultures revealed that SAEC-A3 tended to differentiate towards epithelial-like cells whereas SAEC-H7 tended to differentiate towards neuronal-like cells. Both cell lines were efficiently transfected with pDsRed2-ER and/or pEGFP-N1 plasmids, indicating that they could represent useful biotechnological tools. Daily expression of pcna showed significant expression rhythms, with maximum levels of cell proliferation during the day-night transition. Currently, these cell lines are being successfully used as experimental models for the study of cellular metabolism, physiology and rhythms as well as for toxicological, pharmacological and gene expression analyses.

Salinity-mediated changes in hematological parameters, stress, antioxidant responses, and acetylcholinesterase of juvenile olive flounders (Paralichthys olivaceus)

The purpose of this study was to confirm the limit of salinity tolerance in juvenile olive flounders (Paralichthys olivaceus) by changes in blood parameters, AChE, antioxidant and stress responses. The P. olivaceus (mean weight 38.8 ± 4.2 g and mean length 16.4 ± 1.2 cm) were exposed to different concentrations of salinity (seawater, 16, 8, 4, 2, and 0 psu) for 2 weeks. Plasma osmotic pressure was significantly decreased in the P. olivaceus at 0 psu. Hematological parameters such as hematocrit and hemoglobin were significantly decreased in the P. olivaceus at low salinity. Plasma components also changed significantly in the low salinity environment. As a stress indicator, cortisol was significantly increased at low salinity. SOD and GST antioxidant responses, were significantly increased. GSH level in the liver was significantly increased, whereas a significant decrease was observed in the gill GSH level. AChE was significantly increased in P. olivaceus at low salinity. The results of this study indicate that exposure to salinities lower than 8 psu leads to changes in hematological parameters, neurotransmitter, antioxidant and stress responses of P. olivaceus.

Modeling larval dispersal for the gilthead seabream in the northwestern Mediterranean Sea

To investigate dispersal and connectivity between spawning and lagoon nursery habitats of the gilthead seabream, Sparus aurata, in the Gulf of Lions (northwestern Mediterranean Sea), we modeled the potential transport of the species' larvae between its supposed main spawning site in the region (the Planier Island) and two of its main local nursery areas (the coastal lagoons of Thau and Salses-Leucate). Passive larval drift simulations using a dispersal biophysical model showed a large variability in the possible trajectories from spawning to nursery areas and in the predicted ages for larvae arrival on the two nursery sites. The most common ages at arrival obtained in the simulations (20-60 days) are broadly consistent with previous modeling studies but contrast with the actual ages of the S. aurata post-larvae collected in 2016 and 2017 at time of the lagoon entrances (60-90 days, from otolith readings). The period between 25 and 70 days being critical for gilthead seabream larvae to acquire sufficient swimming, osmoregulatory, and olfactory abilities to enter coastal lagoons, we argue that ontogenic development plays a crucial role in the transport and local retention of S. aurata larvae in the studied region, explaining the discrepancy between simulation results and observed data.

The influence of salinity on the toxicity of Corexit at multiple life stages of Gulf killifish

Following the Deepwater Horizon oil spill, approximately 7 million liters of the dispersant Corexit 9500A were released to promote oil biodegradation by breaking up surface oil slick formation. This process is accomplished via amphipathic anionic surfactants within dispersants that facilitate the mixing of aqueous and lipid phases. However, the amphipathicity of Corexit may also cause it to interact with biological membranes like the gill, impairing gill function and ultimately disrupting physiological processes mediated by it, such as osmoregulation. The goal of this study was to investigate the osmoregulatory effects and toxicity of Corexit in Gulf killifish. Killifish at the embryonic, larval, juvenile, and adult life stages were exposed to Corexit in water of different salinities to assess the interactive effects of ontogeny and salinity on Corexit toxicity. Corexit was not toxic to embryos except when exposed in hyperosmotic water where it had negligible effects; however, its toxicity to killifish increased dramatically following hatch, showing its greatest deleterious effects in adults. Corexit tended to increase sodium and chloride burdens in killifish when exposed in hyperosmotic waters and reduced whole-body and plasma ion concentrations in fish exposed to hypoosmotic waters. However, Corexit exposure at hyperosmotic salinities resulted in an increased differential accumulation of sodium over chloride as killifish matured. These findings suggest that Corexit may impair gill structure or alter specific components of osmoregulatory function, thus impacting osmoregulation in hypersosmotic and hypoosmotic waters, potentially impairing survival during osmotic challenges. Furthermore, the magnitude of these impacts continues to increase concomitant with gill ontogeny.

Molecular endocrine changes of Gh/Igf1 axis in gilthead sea bream (Sparus aurata L.) exposed to different environmental salinities during larvae to post-larvae stages

The influence of acclimation of the euryhaline gilthead sea bream (Sparus aurata) larvae/post-larvae to brackish water on growth, energetic contents, and mRNA levels of selected hormones and growth-regulating hypothalamic neurohormones was assessed. Specimens from 49 days post-hatching were acclimated during 28 days to two different environmental salinities: 38 and 20 psu (as brackish water). Both groups were then transferred to 38 psu and acclimated for an additional week. Early juveniles were sampled after 28 days of acclimation to both salinities and one week after transfer to 38 psu. Pituitary adenylate cyclase-activating peptide (adcyap1; pacap), somatostatin-I (sst1), growth hormone (gh1), insulin-like growth factor-I (igf1), and prolactin (prl) mRNA expression were all studied by QPCR. Post-larvae acclimated to 20 psu showed better growth performance and body energetic content than post-larvae maintained at 38 psu. prl, adcyap1, and igf1 mRNA expression levels increased in 20-psu-acclimated post-larvae but decreased upon transfer to 38 psu. GH1 expression did not show significant changes under both experimental conditions. Our results suggested an enhanced general performance for post-larvae in brackish water, supported by the actions of adcyap1, igf1, and prl.

Natural environmental impacts on teleost immune function

The environment in which teleosts exist can experience considerable change. Short-term changes can occur in relation to tidal movements or adverse weather events. Long-term changes can be caused by anthropogenic impacts such as climate change, which can result in changes to temperature, acidity, salinity and oxygen capacity of aquatic environments. These changes can have important impacts on the physiology of an animal, including its immune system. This can have consequences on the well-being of the animal and its ability to protect against pathogens. This review will look at recent investigations of these types of environmental change on the immune response in teleosts.

Projected habitat loss for Atlantic herring in the Baltic Sea

Projected, climate-driven changes in rainfall patterns are expected to alter the salinity (S) of estuaries and larger brackish water bodies, such as the Baltic Sea. Some marine fish larvae are potentially more sensitive to low salinity than older stages, hence we compared the low salinity tolerance of Atlantic herring (Clupea harengus) larvae at the individual and population levels including four populations in the North and Baltic Seas. Acute low salinity tolerance was similar (S = 1.9-2.7) across populations and increased with increasing body size. Based on this physiological threshold and a regionally down-scaled climate model, spawning habitats in the northern and eastern Baltic Sea are projected to be largely unsuitable for herring by 2100. Although adaptive mechanisms may attenuate the effect in some species, the limited physiological tolerance of fish larvae will remain an important bottleneck for the persistence of marine fish populations in brackish waters undergoing climate-driven freshening.

Microscopic identification of novel cell types in the integument of larval lake sturgeon, Acipenser fulvescens

Osmoregulation, respiration, nutrient/mineral transport, and defense mechanisms are all evident in the integument of fish. The role of the integument in these physiological processes is particularly important during early life history in larval fishes, as functional systems such as the gills and gastrointestinal tract are not fully developed. Using a variety of microscopy techniques, we describe the morphology of keratinocytes, mitochondria rich cells, ciliated cells and mucous cells of the skin, yolk sac, and gills. The cytology we observed was similar to previous studies describing the integument of larval fish, however, we have also identified two novel cell types on the integument of larval Lake Sturgeon, Acipenser fulvescens, between 9 and 34 days post fertilization. Our detailed analysis included a multifaceted microscopy approach using scanning electron, transmission electron, and light microscopy to elucidate the histology of the tissue and cellular morphology in addition to quantification and distribution of these novel cell types. The first cell type had a characteristic ampullary shape with a central cavity and a pore opening at the surface. The second, located on the free surface of the epidermis, had an uneven plasma membrane surface. Based on the abundance of secretory vesicles, organelles necessary for protein synthesis, and the lack of neural connection in both cell types, we propose these cells to be involved in the release of semiochemicals that may act as a pheromone, alarm substance, or chemical defense mechanism.

Ontogeny and osmoregulatory function of the urinary system in the Persian sturgeon, Acipenser persicus (Borodin, 1897)

The structure of the kidney and the localization of Na(+), K(+)-ATPase (NKA) immunopositive cells were examined throughout the postembryonic development of the Persian sturgeon, Acipenser persicus, from newly hatched prelarvae (10mm) to 20 days post hatch (20 DPH) larvae (31mm). Investigations were conducted through histology and immunohistochemistry by using the light and immunofluorescence microscopy. The pronephros was observed in newly hatched prelarvae. The cells lining the distal pronephric tubules and their collecting ducts showed laterally expressed NKA immunofluorescence that later extended throughout the whole cytoplasm. Mesonephrogenous placodes and pre-glomeruli were distinguished at 2 DPH along the collecting ducts posteriorly. Their tubules were formed and present in kidney mesenchyma, differentiated into neck, proximal, distal and collecting segments at 7 DPH when NKA immunopositive cells were observed. Their distal and collecting tubules showed an increasing immunofluorescence throughout their cytoplasm while the glomeruli remained unstained. From D 9 to D 17, the epithelial layer of pronephric collecting duct changed along the mesonephros to form ureters. Ureters, possessing isolated strong NKA immunopositive cells, appeared as two sac-like structures hanging under the trunk kidney. Since NKA immunopositive cells were not observed on the tegument or along the digestive tract of newly hatched prelarva, and also the gills are not formed yet, the pronephros is the only osmoregulatory organ until 4 DPH. At the larval stage, the pronephros and mesonephros are functional osmoregulatory organs and actively reabsorb necessary ions from the filtrate.

Effects of potassium ion supplementation on survival and ion regulation in Gulf killifish Fundulus grandis larvae reared in ion deficient saline waters

Teleost fish often live in an environment in which osmoregulatory mechanisms are critical for survival and largely unknown in larval fish. The effects of a single important marine ion (K(+)) on survival and ion regulation of larval Gulf killifish, an estuarine, euryhaline teleost, were determined. A four-week study was completed in four separate recirculating systems with newly hatched larvae. Salinity in all four systems was maintained between 9.5 and 10‰. Two systems were maintained using crystal salt (99.6% NaCl) with K(+) supplementation (1.31±0.04mmol/L and 2.06±0.04mmol/L K(+); mean±SEM), one was maintained with crystal salt and no K(+) supplementation (0.33±0.05mmol/L K(+)), the fourth system was maintained using a standard marine mix salt (2.96±0.04mmol/L K(+)), the salt mix also included standard ranges of other ions such as calcium and magnesium. Larvae were sampled throughout the experiment for dry mass, Na(+)/K(+)-ATPase (NKA) activity, whole body ion composition, relative gene expression (NKA, Na(+)/K(+)/2Cl(-) cotransporter (NKCC) and cystic fibrosis transmembrane conductance regulator (CFTR)), and immunocytochemistry staining for NKA, NKCC, and CFTR. Larvae stocked into water with no K(+) supplementation resulted in 100% mortality within 24h. Mortality and dry mass were significantly influenced by K(+) concentration (P≤0.05). No differences were observed among treatment groups for NKA activity. At 1dph NKA mRNA expression was higher in the 0.3mmol [K(+)] group than in other treatment groups and at 7dph differences in intestinal NKA and CFTR staining were observed. These data indicate that the rearing of larval Gulf killifish may be possible in ion deficient water utilizing specific ion supplementation.